Various pneumatic tires have been proposed of which at least one component thereof is a rubber composition containing at least one diene-based elastomer, synthetic amorphous silica reinforcement, for example a particulate precipitated silica, for which the silica is coupled to the elastomer by an organopolyalkoxysilane polysulfide or organomercaptoalkoxysilane coupling agent. In general, the alkoxy group moieties of the coupling agent react with hydroxyl groups (e.g. silanol groups) contained on the silica (e.g. precipitated silica), and wherein sulfur atoms from the polysulfide or mercapto moiety interact with the diene-based elastomer(s), to create the coupling effect, a phenomenon well known to those skilled in such art.
Exemplary of such organopolyalkoxysilyl polysulfide coupling agents are, for example, bis(3-trialkoxysilylalkyl)polysulfides which contain an average of from 2 to about 4, alternately an average of from 2 to about 2.6, connecting sulfur atoms in their polysulfidic bridge. At least one of such alkoxy groups may be comprised of a low molecular weight alkoxy group containing from 2 through 4 carbon atoms such as for example, an ethyl, propyl and/an or butyl groups as, for example, an ethoxy, propoxy or butoxy group or their mixtures. The remainder of such alkoxy groups, if any, for such trialkoxy moiety of the coupling agent may be of a higher molecular weight which may contain, for example, from 5 through 18 carbon atoms.
Representative of such coupling agent is, for example, comprised of a bis(3-triethoxysilylpropyl)polysulfide.
Use of such coupling agent is proposed in numerous patent publications, a partial representative example of which are, which is intended to be exemplary and not intended to be inclusive, U.S. Pat. Nos. 4,278,587, 5,696,197 and 6,046,266.
It is well known that the reaction of such alkoxy moiety-containing coupling agent, where its alkoxy groups contain at least one low molecular weight alkoxy group such as for example an ethoxy group in which at least one of the alkoxy substituents is an ethanol radical, reacts with reactive substituents such as for example hydroxyl groups (e.g. silanol groups) contained on the silica (e.g. precipitated silica) wherein a volatile low molecular weight alkyl hydrocarbon alcohol (alkanol) by-product is formed having, for example, from 2 to and including 4 carbon atoms, such as for example ethanol, by the reaction between the aforesaid alkoxy group(s) and hydroxyl group(s).
Historically, elimination, or substantial elimination, of a volatile alcohol (alkanol) by-product within a rubber composition such as, for example, caused by the reaction of an organopolyalkoxysilane polysulfide, or an organoalkoxymercaptosilane, with hydroxyl groups on a precipitated silica in situ within the rubber composition was a proposed pre-treatment of the precipitated silica prior to its addition to the rubber composition. By such method, the alcohol (e.g. ethanol) by-product was produced outside the rubber composition so that the addition of the pre-treated silica to the rubber composition yielded little, if any, of the alcohol by-product in situ within the rubber composition. For example, see U.S. Pat. No. 6,573,324 and U.S. Patent Application No. 2005/0009955.
However, such silica pretreatment involves an additional and separate preparation step(s) for the processing of the silica, coupling agent and rubber composition.
Accordingly, it is desired herein to provide a simpler methodology for preparation of a rubber composition which does not require such additional, separate, preparation step of pre-treating the silica, to inhibit, or retard, the presence of alcohol by-product formed in situ within the rubber composition.
An important aspect of this invention is an inclusion of a dispersion of an alcohol-adsorbing, particularly a low molecular weight alcohol-adsorbing (e.g. ethanol-adsorbing) particulate activated carbon in the diene-based elastomer containing rubber composition to at least partially adsorb the low molecular weight, and relatively volatile, alcohol by-product (e.g. alkanol comprised of ethanol) and to thereby inhibit or retard its evolution into the tire and/or atmosphere.
Activated carbon, in general, can be a very versatile adsorbent for various gases and liquids in a sense that the size and density of its pores can be considerably varied.
Activated carbon can be, for example, a primarily amorphous particulate form of carbon, usually a microcrystalline, non-graphitic form of carbon, having a large surface area and pore volume which can make it useful in providing adsorptive properties for adsorbing various gases and liquids. For example, its average specific surface area (BET nitrogen adsorption) may be in a range of, for example, from about 500 to about 2000 m2/g or even greater. Such surface area is of a significant magnitude greater than the average nitrogen adsorption (BET) surface area in a range of, for example, from about 8 to about 150 m2/g for typical rubber reinforcing carbon blacks and therefore considered herein as being exclusive of such rubber reinforcing carbon blacks.
Commercial grades of activated carbon are often referred to as being gas-phase and liquid-phase adsorbents although the adsorbent abilities may somewhat overlap each other depending upon a particular activated carbon and intended gas and/or liquid to be adsorbed.
Generally, the larger the surface area of the activated carbon, the greater its adsorption capacity with the available surface area of the activated carbon being somewhat dependent upon its pore volume.
Therefore a large surface area may be promoted, for example, by:
(A) maximizing the number of pores of very small dimensions and/or
(B) minimizing the number of pores of very large dimensions.
The pores are often referred to in the sense of their sizes by the International Union of Pure and Applied Chemistry as “micropores”, “mesopores” and “macropores”.
Micropores are referred to as having a pore width of less than 1.8 nm, mesopores having a pore width of from 1.8 to 50 nm and macropores having a pore width of greater than 50 nm. It is the presence and pore size distribution of the micropores and mesopores which are considered to contribute to the adsorptive capacity of the activated carbon. For example, a relatively high pore volume percentage of mesopores (e.g. above 50 percent of the total pore volume) is generally desirable.
Various raw materials may be used as a source for the carbon by carbonizing and then activation such as, for example and not intended to be limited, wood chips, sawdust, lignite, coconut shells, coal and carbon black refuse, to name a few sources.
Various methods of preparing activated carbon may be used. For example activated carbon may be prepared by one of two distinct processes, namely, by
(A) chemical activation, or
(B) thermal activation.
For example, thermal activation typically involves gasification of the carbon at relatively high temperatures, after an initial carbonization of the raw material. For example, chemical activation typically involves chemical dehydration/condensation reactions at significantly lower temperatures. For example, a carbonaceous material such as a lignocellulosic material may be treated with a chemical activation agent such as, for example, phosphoric acid or zinc chloride. Such lignocellulosic material may be, for example, wood chips and/or sawdust. Various method of preparing activated carbon are well known by those having skill in such art.
Various functional groups may be also formed, if desired, during activation of the carbon, for example by interaction of free radicals on the carbon surface, to render the surface of the activated carbon chemically reactive and to thereby further influence its adsorptive abilities and properties.
Activated carbon has been commercially manufactured and marketed for many years as adsorbents for various gasses and liquids (including for, example, use in gas masks and automobile gasoline recovery canisters as well as many other uses) and therefore are well known, as well as various methods of preparation, by those having skill in such art.
Representative examples of various activated carbon as well as applications and methods of preparation may be found, for example, in U.S. Pat. Nos. 5,206,207, 5,212,144, 5,250,491, 6,337,302, 6,863,713 and 6,696,384 (using carboxy methylcellulose post treatment) as well as earlier U.S. Pat. Nos. 2,083,303 and 2,508,474.
Representative of various commercially available activated carbons for various purposes are, for example, activated carbon from the MeadWestvaco company such as, for example, WV-A900, WV-A1100, WV-A1500, BAX950, BAX1100 and BAX1500; activated carbon from the Carbochem company such as, for example CARBOCHEM™ GS-75, GL80, VP-50, LP-30, DC-50, DC-40, LQ-900, LQ-1000, LQ900S, LQ-1240 and CA-10; activated carbon and activated carbon families from the Calgon Carbon Corporation as, for example, Ventsorb™, Vapor Pac™, Cal™, Cane Cal™, CPG™, Filtrasorb™, GW™, MRX™, and WPL-WPH™.
For this invention, it is desired that the activated carbon has an ability (e.g. a suitable combination of surface area and pore size distribution) for adsorbing a low molecular weight alcohol (alkanol) such as for example ethanol, the preparation and use of which is considered herein to be within the ability of a person skilled in the art of activated carbon preparation without undue experimentation.
In practice, it is considered herein that the use of a dispersion of an ethanol-adsorbing activated carbon (e.g. low molecular weight alkanol-adsorbing activated carbon) in a rubber composition containing at least one diene-based elastomer, precipitated silica and organopolyalkoxysilane polysulfide or organoalkoxymercaptosilane, such as, for example, a bis(3-alkoxysilylalkyl)polysulfide for the organopolyalkoxysilane, where at least one of the alkoxy substituents is an ethyl radical in which an ethanol by-product is formed, to thereby adsorb said ethanol by-product is novel and a significant departure from past practice, particularly for a tire component of such rubber composition.
While the mechanism may not be fully understood, an important aspect of the invention is for the inclusion of the dispersion of particulate low molecular weight alcohol (e.g. ethanol) adsorbing activated carbon filler which can adsorb such alcohol (alkanol) and thereby retard or substantially inhibit such alcohol by-product from atmospheric evolution.
In the description of this invention, the term “phr” is used to designate parts by weight of an ingredient per 100 parts of elastomer, including the butyl rubber, unless otherwise indicated. The terms “elastomer” and “rubber” are used interchangeably unless otherwise indicated. The terms “cure” and “vulcanize” are used interchangeably unless otherwise indicated.